The present invention relates to a measuring instrument for measuring a video signal level and a display device for displaying a video signal level. The present invention particularly concerns a waveform monitor for measuring a video signal level and a display device for communicating with the waveform monitor by wireless and displaying a video signal level.
For example, a video shooting process such as the production of TV programs and movies includes a process of illuminating an object with a lighting display device and shooting the object while adjusting the light source intensity of the lighting display device. As a method for confirming whether or not the light source of a lighting display device has a proper intensity, the following are available: a method for measuring a luminance of an illuminated object with a luminance meter, and a method for reading a video signal level by using a waveform monitor which receives a video output signal from a video camera for shooting an object.
In the latter method, a video camera and a lighting display device may be separated from each other. For example, a video camera may be positioned near the floor of a studio and a lighting display device may be positioned near the ceiling of the studio. In this case, the user of the lighting display device uses a long extension cable from the floor to the ceiling of the studio (connects the video output terminal of the video camera and the video input terminal of a waveform monitor via an extension cable), brings the waveform monitor close to the ceiling near the lighting display device, and adjusts the light source intensity of the lighting display device.
In this state, three problems arise as described below. A first problem is the difficulty of bringing a waveform monitor into a working space when the working space is small around the lighting display device. A second problem is that when two or more lighting display devices are provided, after the light source intensity of one of the lighting display devices is adjusted, both a waveform monitor and an extension cable need to be brought close to another lighting display device to adjust the light source intensity of the lighting display device. A third problem is degradation of a video output signal due to a long extension cable.
Furthermore, a fourth problem arises regardless of whether or not a video camera and a lighting display device are separated from each other. The problem is that only the skilled user can readily confirm a video signal level from waveforms shown on the display of a waveform monitor. Namely, only the skilled user can readily locate a required portion of complicated waveforms (waveforms including a luminance and color-difference information are superimposed on each line) shown in FIG. 7b, corresponding to the image of FIG. 7a, and read a luminance of one point (e.g., the position of “+” mark corresponding to reference numeral 71 or 72 of FIG. 7a) in the image while paying attention only to the required portion. In other words, it is difficult for the unskilled user to read a luminance of one point in an image while looking at the waveforms of FIG. 7b. 
Moreover, a video shooting process frequently includes a process of shooting the same object two or more times. In this case, for example, it is necessary to match a video signal level of the first shooting with a video signal level of the subsequent shooting on the position of “+” mark corresponding to reference numeral 71 of FIG. 7a. Therefore, a fifth problem is that only the skilled user can readily match video signal levels while looking at the waveforms of FIG. 7b. 
In the application, the applicant indicated Patent Document 1 as a related invention of the present invention.
[Patent Document 1]
Japanese Patent Laid-Open No. 10-340133 (pages 2 to 3, FIG. 2)